It's in the 'stdwin' subdirectory of the Lib directory. (Surprise!)
To add this directory permanently to your module search path, you have
to uncomment a line beginning with #STDWINPATH= in the Modules/Setup
file.
BTW this is my mistake -- the line for STDWINPATH in the Setup file is
far away from the other lines for STDWIN. Will be corrected in 1.1.
--Guido van Rossum, CWI, Amsterdam <Guido.van.Rossum@cwi.nl>
<URL:http://www.cwi.nl/cwi/people/Guido.van.Rossum.html>